1. Field
The present disclosure relates generally to calibrating sensors such as, for example, photosensors, which have pixel-dependent noise or bias.
2. Description of Related Art
Photosensors can be used to detect the amount of light incident on the image sensor. Photosensors include, for example, devices such as charge-coupled devices (CCDs) in which each pixel includes a photoactive capacitor, and active pixel image sensors in which each pixel includes a light sensor and an active amplifier. The amplifier can provide a programmable or switchable gain for each pixel. Active pixel image sensors produced by complementary metal-oxide-semiconductor (CMOS) techniques are commonly known as CMOS sensors. Generally, the amount of electric current produced by a pixel of the photosensor increases with the amount of light incident on the pixel. However, even when no light is incident on the pixel, a small amount of electric current, commonly called “dark current,” can flow from the pixel. When an image is taken with a photosensor, dark current can act as a source of noise in the resulting image. Dark current noise can be reduced by using dark-frame subtraction in which a dark field image, taken with little or no light incident on the sensor, is subtracted from the image to at least partially compensate for the noise produced by the dark current.